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Subcellular Localization and Characterization of Neuronal Nitric Oxide Synthase
Author(s) -
Hecker Markus,
Mülsch Alexander,
Busse Rudi
Publication year - 1994
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1994.62041524.x
Subject(s) - nitric oxide synthase , biochemistry , endoplasmic reticulum , atp synthase , calmodulin , microsome , enzyme , subcellular localization , biology , intracellular , myristoylation , chemistry , microbiology and biotechnology , membrane , cytoplasm
In contrast to the predominantly participate, Ca 2+ /calmodulin‐dependent nitric oxide (NO) synthase in endothelial cells, the corresponding neuronal isoenzyme is considered to be mainly soluble, presumably owing to the lack of a posttranslational myristoylation. However, preliminary findings from this and other laboratories suggest that a substantial portion of the neuronal NO synthase activity may in fact be membrane bound. We have therefore investigated the distribution of this enzyme among subcellular fractions of the rat and rabbit cerebellum in more detail. Up to 60% of the total NO synthase activity was found in the particulate fraction and, according to density gradient ultracentrifugation, associated mainly with the endoplasmic reticulum fraction. There was no apparent difference between the soluble and particulate enzymes with respect to their specific activity, Ca 2+ and pH dependency, inhibitor sensitivity, or immunoreactivity, suggesting that both rat and rabbit cerebella contain a single Ca 2+ /calmodulin‐dependent NO synthase. The inhibition by the cytochrome P450 inhibitor SKF‐525A of the NO synthase activity in these subcellular fractions (IC 50 = 90 μ M ) and the fact that mammalian cytochrome P450 enzymes are endoplasmic reticulum‐bound proteins support the notion that the cerebellar NO synthase is a cytochrome P450‐type hemoprotein. Moreover, the aforementioned findings suggest that posttranslational myristoylation may not be the only factor determining the intracellular localization of NO synthase.